ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 415 





Arrangement (solitary, in clusters, in whorls, etc. ; give 

 number) . 



( as to movement (stagnant, quiet, rapid, torren- 

 Water ) tial, etc.) 



( as to oxygen content. 



The record of this study will be contained in the completed 

 table . 



2. Phylogenetic adaptation in diving beetles. 



We will now study 

 the adaptation to a 

 changed environment of 

 a series of forms of com- 

 mon origin. For that 

 fi purpose it would be hard 

 ' to find better material 

 than that furnished by 

 | the family Dytiscidae of 

 diving beetles (fig. 244). 

 Almost any permanent 

 pond will furnish a num- 

 ber of forms that differ 

 i in size and habit, and 

 ! that exhibit different 

 degrees and kinds of 

 specialization. We will 

 study the adaptation of the adult beetles to pond life. 



These beetles have fully retained their terrestrial mode 

 of respiration. They take in air through abdominal 

 spiracles situated on the back of the abdomen, underneath 

 the wing covers. They have merely adopted improved 

 means of carrying air with them when they descend beneath 

 the surface of the water. 





FIG. 244. A 



imerrogatus). 



